In addition to providing printed telephone directories, telephone companies provide telephone directory assistance services. Users of these services call predetermined telephone numbers and are connected to directory assistance operators. The operators access directory databases to locate the directory listings requested by the users, and release the telephone numbers of those listings to the users.
Because telephone companies handle a very large number of directory assistance calls per year, the associated labor costs are very significant. Consequently, telephone companies and telephone equipment manufacturers have devoted considerable effort to the development of systems which reduce the labor costs associated with providing directory assistance services.
In a typical directory assistance system the caller is first prompted to provide listing information, in other words to specify in what area resides the business or individual whose telephone number he seeks. If valid speech is detected, the speech recognition layer is invoked in an attempt to recognize the unknown utterance. On a first pass search, a fast match algorithm is used so select the top N orthography groups from a speech recognition dictionary. In a second pass the individual orthographies from the selected groups are re-scored using a more precise likelihood. The top orthography in each of she top two groups are then processed by a rejection algorithm which evaluates if they are sufficiently distinctive from one another so the top choice candidate can be considered to be a valid recognition.
Once the ton choice orthography has been validated by the rejection layer the link established between the orthography and the corresponding entry in the white pages listing of the telephone company is looked at to derive the telephone number of the entity to which the link points to. This situation is very simple and once the correct orthography in the speech recognition dictionary has been identified deriving the corresponding telephone number is easy. In other instances, however, one orthography may point to several entries in the white pages listing. This is typical for complex organizational structures that normally include a root from which originate several leaves. For example, the stores chain "My store" may have several outlets in a metropolitan area. Thus, if the user formulates his request by saying "My store" the speech recognition layer will identify the orthography "My store" as being the most likely match for the spoken utterance. There is, however, no way of knowing which outlet at that particular chain the user is actually seeking. Since any one of the outlets presents a distinct possibility of being the intended entity the orthography "My store" is linked to all entries in the white pages corresponding to the various outlets of the chain.
One possibility of resolution is to use a navigation scheme where the system audibly plays back to the caller a list of possibilities and requests an indication about which one he seeks. This approach to link resolution is not necessarily the best since it requires complex navigational schemes and may annoy the user particularly when the number of links is important. Indeed, the user may be forced to listen for a comparatively long time to a multiple choice question before the requested telephone number can be released.
Thus, there exists a need in the industry to develop an automated directory assistance system that can predict with a reasonable degree of accuracy what link should be selected when an orthography points toward several entries in the white pages listing.